The present invention relates to an FM multiplex broadcasting receiver and a method of retaining received data in the FM multiplex broadcasting receiver.
FM multiplex broadcasting is for broadcasting voices, characters, figures together with stereo voices, that is, one for multiplexing voices, characters and figures on normal FM broadcasting and broadcasting the multiplexed voices, characters and figures.
Typical examples of the standard of the FM multiplex broadcasting include three systems, that is, DARC (Data Radio Channel), a fixed receiving system, and RDS (Radio Data System). The DARC is the newest, and is employed as an international standard. The DARC is described in accordance with xe2x80x9cReference Model of Data Broadcastingxe2x80x9d in Recommendation 807 of ITU-R (International Telecommunication Union).
The DARC is for converting characters and figures into digital information, modulating a sub-carrier frequency of 76 kHz and frequency-multiplexing the sub-carrier frequency on a stereo base band signal, frequency-modulating the multiplexed signal, and broadcasting the frequency-modulated multiplexed signal.
FIG. 6 illustrates a layer structure representing a character/figure coding system of the DARC.
A layer 1 specifies transmission path characteristics. A sub-carrier signal is superimposed on the side of higher frequencies than those of an L+R signal and an Lxe2x88x92R signal which are normal FM stereo broadcasting signals. Modulation method of sub-carrier employs an LMSK (Level-controlled Minimum Shift Keying) method for controlling the level of a sub-carrier by the degree of modulation of the Lxe2x88x92R signal in consideration of the fact that the interference of the sub-carrier with a voice signal becomes significant when the degree of voice modulation is small.
A layer 2 defines a frame structure of data including an error-correcting system. Each of frames is composed of 272 blocks in the column direction, and a 16-bit block identification code (BIC) is added to the head thereof. Frame synchronization and block synchronization are achieved on the basis of the block identification code. 190 blocks out of the 272 blocks in the column direction are a packet for transmitting data, and 82 blocks are a parity packet for transmitting a parity in the vertical direction. Each of the packets is composed of a 176-bit data portion, 14-bit CRC (Cyclic Redundancy Code) which is an error-detecting code and a 82-bit horizontal parity portion in the row direction.
Transmitted data is first subjected to error correction in a step of the layer 2 with its one frame as a basic unit. In practice, the transmitted data is sent out in a frame structure in which packets and parity packets are arranged again in a predetermined order in the longitudinal direction, as shown in FIG. 7.
A layer 3 defines the structure of a data packet. The data packet is composed of 176 bits excluding BIC, CRC and a parity in each row in a frame. The data packet is composed of a prefix and a data block.
A layer 4 indicates the structure of a data group. The data group is composed of one or a plurality of data blocks. The data group also includes CRC which is an error-detecting code. The transmitted data is also subjected to error detection in the layer 4. One of the data groups corresponds to data on one page.
A layer 5 defines the structure of a bundle of information transmitted by FM multiplex broadcasting, that is, program data.
FIG. 8 illustrates using functional blocks the schematic construction of an FM multiplex broadcasting receiver utilizing a personal computer.
The FM multiplex broadcasting receiver comprises a tuner 301, a sub-carrier data receiving LSI302 a receiving processing unit 303, a program reconstructing unit 304, a program analyzing unit 305, a display processing unit 306, a plotting unit 307, and a display 308. In an FM multiplex broadcasting receiver utilizing a personal computer, the tuner 301, the sub-carrier data receiving LSI 302, and the receiving processing unit 303 are constituted by a PC card or the like. Further, the program reconstructing unit 304, the program analyzing unit 305, the display processing unit 306, the plotting unit 307, and the display 308 are constituted by the personal computer.
The sub-carrier data receiving LSI 302 performs LMSK demodulation and error correction on the basis of an output from the tuner 301. In the sub-carrier data receiving LSI 302, signals of a layer 1 is converted into data of a layer 2.
The receiving processing unit 303 accepts required ones of data in block units outputted from the LSI 302. In the receiving processing unit 303, the data of the layer 2 is converted into data of a layer 3.
The program reconstructing unit 304 reconstructs a program. In the program reconstructing unit 304, the data of the layer 3 is converted into data of a layer 4.
The program analyzing unit 305 performs decoding processing conforming to an eight level coding system. In the program analyzing unit 305, the data of the layer 4 is converted into data of a layer 6 (the eight-bit coding system).
The display processing unit 306 acquires a plotting pattern, and subjects the plotting pattern to various types of processing. The plotting unit 307 outputs the plotting pattern obtained by the display processing unit 306 to the display 308.
In the FM multiplex broadcasting receiver, examples of a method of retaining a received program in a data format which can be versatily recorded and reproduced include a method of retaining text data obtained by the program analyzing unit 305 and a method of retaining bit map data obtained by the display processing unit 306.
When the received program is stored in a text format or a bit map format, information representing the hierarchical structure of the program, selection of the program, a plotting operation, and the like cannot be retained, whereby the original program at the time of receiving cannot be faithfully reproduced.
Therefore, it is considered that only the data of the layer 4 obtained by the program reconstructing unit 304 is retained. When only the data of the layer 4 is stored, however, there is no prefix including data representing service identification or the like, whereby the original program at the time of receiving cannot be faithfully reproduced. In the FM multiplex broadcasting receiver, when the data of the layer 4 is retained in a RAM, it is retained in the RAM in its own method such that the prefix is reflected. A system for storing the data of the layer 4 in the RAM is not standardized in all FM multiplex broadcasting receivers.
An object of the present invention is to provide an FM multiplex broadcasting receiver capable of retaining a received program in such a data format that the original program at the time of receiving can be faithfully reproduced by various types of applications for reproducing FM multiplex broadcasting and a method of retaining received data in the FM multiplex broadcasting receiver.
An FM multiplex broadcasting receiver according to the present invention is characterized by comprising means for storing in first storage means a prefix corresponding to a data block at the head of each of data groups of a received FM multiplex broadcast program and data of a layer 4 of the received FM multiplex broadcast program, an input device for entering a data retention command, and means for producing the data of the layer 3 on the basis of the prefix and the data of the layer 4 which are stored in the first storage means when the data retention command is entered and retaining in second storage means the produced data of the layer 3 as versatile recording and reproducing data.
The first storage means and the second storage means may be the same storage device.
A method of retaining received data in an FM multiplex broadcasting receiver according to the present invention is characterized by comprising the steps of storing in first storage means a prefix corresponding to a data block at the head of each of data groups of a received FM multiplex broadcast program and data of a layer 4 of the received FM multiplex broadcast program, and producing the data of the layer 3 on the basis of the prefix and the data of the layer 4 which are stored in the first storage means when a data retention command is entered and retaining in second storage means the produced data of the layer 3 as versatile recording and reproducing data.
The first storage means and the second storage means may be the same storage device.